Evaluation of airgap structures produced by wet etch of sacrificial dielectrics: Impact of wet etch media on diffusion barriers, copper, and the Cu/SiC:H interface

With the device scaling towards 32 nm node, airgaps have become an attractive alternative to low-k integration. One of the main approaches for airgap formation is sacrificial etch of SiO2 by HF wet chemistry. This paper discusses the impact of HF wet etch media on different conductive diffusion barrier (TiNx, TaNx, WNx) and copper films. Moreover, the impact of sacrificial etch on the interfaces SiC:H/Cu and SiCN:H/Cu is examined. It is shown, that well balanced HF concentration, treatment temperature and exposure time ensure reliable airgap formation with a minimized degradation of the conductive materials. Furthermore it is demonstrated that NH3 plasma treatments lead to a significant improvement of the SiC(N)/Cu interfaces in terms of their resistance to HF chemistry.